Digital projectors typically include an illumination system, some type of spatial light modulator (SLM), and a projection lens. The illumination system generally includes a light source which generates light and a reflector which directs the light from the light source to the SLM. The SLM forms an image beam by modulating the light, either via reflection (e.g. a digital micro-mirror device (DMD)) or transmission (e.g. a liquid crystal modulator), based on image data representative of a desired image to be projected.
The projection lens receives and projects the image beam onto a surface, such as a projection screen, for viewing of the desired image. The projection lens is typically designed to provide a desired magnification, or range of magnifications (i.e. zoom lens) and to minimize optical aberrations (such as chromatic aberrations, lateral color, coma, diffraction, and distortion, for example) in order to provide a high quality projected image. In efforts to minimize such aberrations, projection lenses typically comprise complex systems of multiple lens elements arranged in a particular sequence. Such projection lenses are costly and consume a relatively large amount of space within the projector.
To ease tolerance requirements and thereby simplify projection lens design, some DMD projectors include on-board processing to pre-correct image data to compensate for certain optical aberrations and projection distortions (such as keystone distortion, for example). However, real time pre-correction of such distortion requires significant and costly on-board signal processing capabilities.